+/**
+ * modest_tny_msg_estimate_size:
+ * @plain_body: a string
+ * @html_body: a string
+ * @parts_number: a gint (number of additional parts)
+ * @parts_size: a guint64 (sum of size of the additional parts)
+ *
+ * Estimates the size of the resulting message obtained from the size of the body
+ * parts, and adding the estimation of size headers.
+ */
+guint64
+modest_tny_msg_estimate_size (const gchar *plain_body, const gchar *html_body,
+ guint64 parts_count,
+ guint64 parts_size);